The present invention relates to subterranean well cementing operations and, more particularly, to methods of cementing using cement compositions comprising basalt fibers.
Hydraulic cement compositions commonly are utilized in subterranean operations, particularly subterranean well completion and remedial operations. For example, hydraulic cement compositions are used in primary cementing operations whereby pipe strings, such as casing and liners, are cemented in well bores. In performing primary cementing, a hydraulic cement composition may be pumped into an annulus between the walls of a well bore and the exterior surface of the pipe string disposed therein. The cement composition sets in the annular space, thereby forming therein an annular sheath of hardened, substantially impermeable cement that supports and positions the pipe string in the well bore and bonds the exterior surface of the pipe string to the walls of the well bore. Hydraulic cement compositions also may be used in remedial cementing operations, such as plugging well bores, plugging highly permeable zones or fractures in well bores, plugging cracks and holes in pipe strings, and the like.
Once set, the cement sheath may be subjected to a variety of shear, tensile, impact, flexural, and compressive stresses that may lead to failure of the cement sheath, resulting, inter alia, in fractures, cracks, and/or debonding of the cement sheath from the pipe string and/or the formation. This may lead to undesirable consequences such as lost production, environmental pollution, hazardous rig operations resulting from unexpected fluid flow from the formation caused by the loss of zonal isolation, and/or hazardous production operations. Cement failures may be particularly problematic in high temperature wells, where fluids injected into the wells or produced from the wells by way of the well bore may cause the temperature of any fluids trapped within the annulus to increase. Furthermore, high fluid pressures and/or temperatures inside the pipe string may cause additional problems during testing, perforation, fluid injection, and/or fluid production. If the pressure and/or temperature inside the pipe string increases, the pipe may expand and stress the surrounding cement sheath. This may cause the cement sheath to crack, or the bond between the outside surface of the pipe string and the cement sheath to fail, thereby breaking the hydraulic seal between the two. Furthermore, high temperature differentials created during production or injection of high temperature fluids through the well bore may cause fluids trapped in the cement sheath to thermally expand, causing high pressures within the sheath itself. Additionally, failure of the cement sheath also may be caused by forces exerted by shifts in subterranean formations surrounding the well bore, cement erosion, and repeated impacts from the drill bit and the drill pipe.
To counteract these problems associated with the fracturing and/or cracking of the cement sheath, fibers may be included in the cement composition. Various types of fibers have been used heretofore, including those formed of polypropylene, polyester, polyamide, polyethylene, polyolefin, glass, iron, and steel. These fibers may function to control shrinkage cracking in the early stages of the cement setting process, and also may provide resiliency, ductility, and toughness to the set cement composition so that it resists cracking or fracturing. Further, if fracturing or cracking does occur, the fibers may function to hold the set cement composition together, thereby resisting fall back of the cement sheath. Additionally, fiber may act as lost circulation materials. However, as the cement composition sets, it releases hydrated lime, which may leach out or form alpha dicalcium silicate hydrate, resulting in increased permeability and porosity and decreased compressive strength. While synthetic fibers, such as polypropylene fibers, polyester fibers, and the like, may act to enhance the resiliency and ductility of the set cement composition, these synthetic fibers generally do not enhance compressive strength of the set cement composition or counteract the effects of the hydrated lime. Further, glass fibers may undesirably interact with the hydrated lime that is released during the setting of the cement composition; for example, the alkaline environment created by the hydrated lime may dissolve the glass fibers present in the cement composition.